Electronic lighting control responsive to ambient light

ABSTRACT

In the disclosed control, a light source is turned on and off bistably in response to ambient light. To do this, a photoresistor or photocell, whose resistance increases with decreasing light, is exposed to the ambient light. The photoresistor or cell forms part of a voltage-energized voltage divider, and is connected across a neon lamp from which the cell is shielded. When the ambient light is sufficiently dim the lamp is lit. The current through the neon lamp is intensified with a second photoresistor or photocell in series with the lamp and subject to decreasing resistance as the lamp brightens. This constitutes a positive feedback and holds the neon lamp on. A third photoresistor or photocell in series with a switch responds to the bright lamp to turn on the switch and hence the light source. When the ambient light reduces beyond a given threshold the first photocell turns off the lamp and the second photocell increases its resistance enough to hold off the lamp.

United States Patent 91 Beling [54] ELECTRONIC LIGHTING CONTROLRESPONSIVE TO AMBIENT LIGHT [75] Inventor: Thomas E. Beling, Saxonville,Mass.

[ May 22, 1973 Primary m srrwelt t Stsqlx s n Att0mey David Toren andBernard X. McGeady ABSTRACT In the disclosed control, a light source isturned on and off bistably in response to ambient light. To do this, aphotoresistor or photocell, whose resistance increases with decreasinglight, is exposed to the ambient light. The photoresistor or cell formspart of a voltage-energized voltage divider, and is connected across aneon lamp from which the cell is shielded. When the ambient light issufficiently dim the lamp is lit. The current through the neon lamp isintensified with a second photoresistor or photocell in series with thelamp and subject to decreasing resistance as the lamp brightens. Thisconstitutes a positive feedback and holds the neon lamp on. A thirdphotoresistor or photocell in series with a switch responds to thebright lamp to turn on the switch and hence the light source. When theambient light reduces beyond a given threshold the first photocell turnsoff the lamp and the second photocell increases its resistance enough tohold off the lamp.

19 Claims, 2 Drawing Figures [73] Assignee: Sigma Instruments, Inc.,South Braintree, Mass.

[22] Filed: Sept. 1, 1971 [21] Appl. No.: 176,808

[52] U.S. Cl ..250/214 R, 250/209, 315/159 [51] Int. Cl. ..H0lj 39/12[58] Field of Search ..250/206, 214 R, 209, 250/208, 205;315/151,158,159,156; 307/1 17, 31 1 [56] References Cited UNITED STATES PATENTS3,633,036 1/1972 Nuckalls ..315/159 X 3,483,430 12/1969 Nuckalls et a1...250/209 X 3,042,807 7/1962 Vize ..250/213 A 3,392,284 7/1968 Cain..250/206 X 3,416,032 12/1968 Jahns et al. ..250/205 X PATENTEb 512219753,735,141

THOMAS E. BELING INVENIOR.

ATTORNEYS ELECTRONIC LIGHTING CONTROL RESPONSIVE TO AMBIENT LIGHTBACKGROUND OF THE INVENTION This invention relates to electroniclighting controls, and particularly to electronic lighting controls thatturn a light on and off when ambient light levels are such thatadditional lighting is desired.

Such devices generally employ a photosensitive cell which detectschanges in ambient light and then controls a switching device, such asan electromechanical relay or a solid state device. The relay or thesolid state device accomplishes the appropriate switching of the lights.

One of the difficulties in the manufacture of such devices is the factthat it is, as a practical matter, necessary to achieve a snap action inthe switching operation despite the fact that the illumination level maychange gradually. An example of such gradual change occurs in thenatural light level at twilight or dawn.

The need for a snap action arises for a number of reasons. In anelectromechanical relay, contact chatter caused by slow closure inresponse to gradual changes in the illumination level will damage ordestroy the contacts. With a solid state device, such as a Triac switch,a slow change from off to the on condition will frequently result in anonsymmetrical output waveform which contains an average value, that isto say direct voltage, component. This average value component is notacceptable for use with systems such as mercury vapor lamps utilizinginductive type ballasts. An average value on the incoming waveform 'willresult in ex cessive current flow and damage to the solid state switch.

When using electromechanical relays, the snap action problem is commonlyresolved by designing and adjusting the relays critically. In a solidstate switch, some electronic means of introducing hysteresis, such as aSchmitt trigger is commonly used. However, a Schmitt trigger has somedisadvantages in this connection.

An object of this invention is to improve lighting controls. Anotherobject of this invention is to introduce improved means forproducing-snap action in lighting controls.

SUMMARY OF THE INVENTION According to a feature of this invention, theseobjects are attained and the disadvantages of the prior art obviated, inlighting control for turning an illuminating source on and off inresponse to ambient light conditions, by energizing light means withfirst photoelectric means responsive to the ambient light so as to turnthe light means brighter or dimmer. Second photoelectric meansresponsive to the light means and electrically connected to the lightmeans make the light means brighter as the light means turns bright anddimmer as it turns dim. Control means responsive to the condition of thelight means turn the source on and off. The second photoelectric means,by responding to the light means, produces a positive feedback thatassures a bistable lighting condition.

According to another feature of the invention the first photoelectricmeans is such that the light means becomes brighter as said firstphotoelectric means is subject to less ambient light.

According to another feature of the invention the second photoelectricmeans includes a photoelectric resistor in series with the light meansand responsive to lower its resistance when subjected to more light fromthe light means.

According to another feature of the invention the photoelectric meansincludes a voltage divider adapted to be connected across a voltagesource and having a photoresistor connected across the light means so asto increase the voltage across the light means when the ambient lightdecreases.

According to yet another feature of the invention the light meansincludes a voltage breakdown device.

According to still another feature of the invention the control meansincludes third photoelectric means responsive to the light means andsignal responsive means connected in series with the third photoelectricmeans. The third photoelectric means decreases its resistance inresponse to light from the light means so as to increase the signal tothe signal responsive means as the light from the light means becomesbrighter.

According to yet another feature of the invention the signal responsivemeans includes a relay coil forming part of the relay.

According to yet another feature of the invention the signal responsivemeans includes a semiconductor switch.

According to still another feature of the invention the breakdown deviceincludes a neon lamp.

These and other features of the invention are pointed out in the claims.Other objects and advantages of the invention will become obvious fromthe following detailed description when read in light of theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic circuit diagramof an electronic lighting control embodying features of the invention;and

FIG. 2 is a schematic circuit diagram of another electronic lightingcontrol embodying features of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 1 an alternatingsource AC forms a varying potential across a neon lamp NL by means of avoltage divider composed of a resistor R1 and a photocell P1 whichresponds to ambient light. The voltage across the neon lamp NL thuscorresponds to the voltage appearing across the photocell PlrThephotocell P1 is such as to increase its resistance as the ambient lightdecreases. As a result when the ambient light decreases the increasedresistance places a higher and higher sistor R2. As the illumination ofthe photocell P2 by the neon lamp NL occurs it decreases the resistanceof the photocell P2 thereby allowing greater current flow through thelamp NL. This intensifies the brightness of the neon lamp NL anddecreases the resistance of photocell P2 even further. This regenerativeprocess has the effect of producing the desired snap action.

Firing of the neon lamp NL also illuminates the photocell P3. The latterapplies a control current to the control terminal of a switching deviceSW. According to one embodiment of the invention the switching device SWis a Triac. According to another embodiment it is any type of thyristor.The lowered resistance of the photocell P3 allows sufiicient current toflow into the gate of the switching device SW from the AC source to fireit. As can be seen, when the fired neon lamp NL illuminates thephotocell P3 the resistance of the photocell P3 declines, thus raisingthe current at the gate or control terminal of the switching device SW.This turns on the switching device SW and allows the voltage source ACto apply its voltage across the light source L8 to be controlled. Thisturns on the light source rapidly with the snap action and without theneed for expensive equipment to produce the snap action.

The illumination of the photocell P2 by the neon lamp .NL holds thephotocell P3 in its low resistance condition. Thus, it applies itstum-on current to the switching device SW continuously from thealternating source AC.

A resistor R3 and a capacitor C connected in series across the lightsource LS served as snubbing components to allow the Triac switchingdevice to operate into an inductive circuit such as a typical ballast.

As the ambient light level increases the resistance of the photocell P1,and hence the voltage across the photocell Pl decreases. Eventually apoint will be reached where the voltage across the photocell P1 andhence the neon lamp NL, will diminish the light intensity from the neonlamp. As the light output decreases the resistance of photocell P2increases. This further decreases the light output of the lamp NL byincreasing the series resistance and reducing the current available tothe lamp NL. This regenerative action quickly drives the light output ofthe lamp NL to zero. It increases the resistance of the photocell P3 soas to reduce the control current of the Triac switching device SW. Itturns off the triac switching device and at the same time turns off thelight source LS.

According to one embodiment of the invention a resistor is added fromthe control electrode or gate of the switching device SW to ground. Thisallows the switching device to be controlled on the basis of a controlvoltage rather than a control current.

The light source LS according to the invention may be any type of lightsource such as a fluorescent light source or incandescent light sourceor mercury vapor light source).

Because of the regenerative action of the photocell P2 and the neon lampNL, the neon lamp may, according to another embodiment of the invention,be replaced by a non-firing lamp such as an incandescent lamp.

In FIG. 1 an optical shield S surrounds the photocells P2 and P3 as wellas the neon lamp NL so as to shield the photocells from ambient lightand expose them more intimately to the light from the lamp NL. On theother hand the photocell P1 is exposed to the ambient light.

The resistance of the resistor R2, as well as the resistance of thephotocell P2, are sufficiently high to prev ventfiring of the neon lampin the absence of a sufficient voltage across the photocell P1, withwhich they form a voltage divider.

The control system in FIG. 2 corresponds substantially to that inFIG. 1. Here again the photocell P1 is exposed to ambient light. Itforms part of a voltage divider with the resistor R1 across the voltagesource AC. When the ambient light striking the photocell P1 issufficiently low the resistance of the photocell Pl becomes sufiicientlyhigh to apply a firing voltage to the neon lamp NL. As in FIG. 1 theneon lamp NL, together with the photocells P2 and P3 are shielded by anoptical shield S. Firing of the neon lamp NL illuminates the photocellsP2 and P3 so that their resistances decrease. This decrease in theresistance of the photocell P2 allows more current to flow through theneon lamp NL and intensify its light output. This further exposes thephotocell P2 to more light and again increases the current. Thisregenerative action keeps the neon lamp brightly lit and the resistancesof the photocells P2 and P3 low. This corresponds to the operation ofFIG. 1.

The low resistance of the photocell P3 allows the source AC to apply aholding current to the coil of a relay K1. Because of the regenerativeaction of the photocell P2 and the neon lamp N L, the neon lamp NL issufficiently bright to keep the resistance of the photocell P3 lowenough to allow flow of an actuating current through the coil of therelay K1. This actuating current pulls in the contact T1 of the relay K1and completes the circuit from the source AC to the light L5. The lightLS corresponds to that of FIG. 1.

As the ambient light level increases, eventually a point will be reachedwhere the light intensity of the neon light diminishes because of theshunting action of the photocell P1. As the light output decreases theresistance of the photocell P2 increases, thereby further decreasing thelight output. This regenerative action quickly drives the light outputof the neon lamp NL to zero and sharply raises the resistance of thephotocell P3. This cuts off the current to the coil of the relay Kl. Thecontact T1 opens and the source LS is extin guished.

It should be noted in FIGS. 1 and 2 that the regenerative action causesthe current applied to the switching device SW and the coil of the relayKl to snap or change in the manner of a step function. The currentthrough the photocell P3 is either very small or very large. The neonlamp is either very bright or extinguished.

According to another embodiment of the invention the photocells P1, P2and P3 are constructed on a single substrate with suitableinterconnections and light isolation by the shield S.

As stated, the light source LS may be of any type such as a mercuryvapor lamp, a fluorescent lamp, or an incandescent lamp. It may have anynumber of purposes such as to illuminate streets through the night orilluminate a household.

According to one or more embodiments of the invention the componentsshown in FIGS. 1 and 2 have the following values or descriptions:

P1 Cadmium Sulfide Photocell P2 Cadmium Sulfide Photocell P3 CadmiumSulfide Photocell SW TRIAC C 0.1 uf

AC 120 V RMS K1 l V AC Relay T Relay Contacts While embodiments of theinvention have been described in detail it will be obvious to thoseskilled in the art that the invention may be embodied otherwise withoutdeparting from its spirit and scope.

What is claimed is:

1. A lighting control for turning an illuminating source on and off inresponse to ambient light conditions, comprising first photoelectricmeans responsive to the ambient light, regenerative means coupled tosaid first photoelectric means for assuming one condition when theambient light on said first photoelectric means exceeds a given valueand for assuming a second condition when the ambient light on said firstphotoelectric means is less than a given value, said regenerative meansincluding light means coupled to said first photoelectric means forturning brighter or dimmer in response to the first photoelectric means,said regenerative means further including second photoelectric meansresponsive to light from said light means and electrically coupled tosaid light means for making said light means brighter as said lightmeans turns bright and dimmer as said light means turns dim, and controlmeans coupled to said regenerative means and responsive to the conditionof said regenerative means for turning the source on or off.

2. A control as in claim 1, wherein said light means becomes brighter assaid first photoelectric means is subject to less ambient light.

3. A control as in claim 1, wherein said second photoelectric meansincludes a photoelectric resistor in series with said light means andresponsive to lower its resistance when subjected to more light fromsaid light means.

4. A control as in claim 2, wherein said second photoelectric meansincludes a photoelectric resistor in series with said light means andresponsive to lower its resistance when subjected to more light fromsaid light means.

5. A control as in claim 1, wherein said first photoelectric meansincludes a voltage divider adapted to be connected across a voltagesource and having a variable resistance photocell connected across saidlight means so as to increase the voltage across said light means whenthe ambient light increases.

6. A control as in claim 3, wherein said first photoelectric meansincludes a voltage divider adapted to be connected across a voltagesource and having a variable resistance photocell connected across saidlight means so as to increase the voltage across said light means whenthe ambient light increases.

7. A control as in claim 1, wherein said light means includes a voltagebreakdown device.

8. A control as in claim 7, wherein said second photoelectric meansincludes a photoelectric resistor in series with said light means andresponsive to lower its resistance when subjected to more light fromsaid light means.

9. A control as in claim 7, wherein said second photoelectric meansincludes a photoelectric resistor in series with said light means andresponsive to lower its resistance when subjected to more light fromsaid light means.

10. A control as in claim 7, wherein said first photoelectric meansincludes a voltage divider adapted to be connected across a voltagesource and having a variable resistance photocell connected across saidlight means so as to increase the voltage across said light means whenthe ambient light increases.

11. A control as in claim 1, wherein said control means includes thirdphotoelectric means optically coupled and responsive to said light meansand signal responsive means connected in series with said thirdphotoelectric means, said third photoelectric means decreasing itsresistance in response to light from said light means so as to increasethe signal to said signal responsive means as said light becomesbrighter.

12. A control as in claim 11, wherein said signal responsive meansincludes a relay coil forming a part of a relay.

13. A control as in claim 11, wherein said current responsive meansincludes a semiconductor switch.

14. A control as in claim 7, wherein said breakdown device includes aneon lamp.

15. A control as in claim 1 1, wherein said light means becomes brighteras said first photoelectric means is subject to less ambient light.

16. A control as in claim 11, wherein said second photoelectric meansincludes a photoelectric resistor in series with said light means andresponsive to lower its resistance when subjected to more light fromsaid light means.

17. A control as in claim 15, wherein said second photoelectric meansincludes a photoelectric resistor in series with said light means andresponsive to lower its resistance when subjected to more light fromsaid light means.

18. A control as in claim 1 1, wherein said first photoelectric meansincludes a voltage divider adapted to be connected across a voltagesource and having a variable resistance photocell connected across saidlight means so as to increase the voltage across said light means whenthe ambient light increases.

19. A lighting control for turning an illumination source on and off inresponse to ambient light conditions, comprising photoelectric meansresponsive to the ambient light, said photoelectric means assumingvariable electrical conditions in response to variation of the ambientlight conditions, light component means coupled to said photoelectricmeans for producing varying conditions of brightness in response tochanges in the electrical condition of said photoelectric means,photoelectric component means close enough to the light component meansto be responsive to light therefrom and exhibiting electrical conditionswhich vary in response to light incident thereon and regenerativelycoupled to said light component means for making the light from saidlight component means even brighter as the light turns bright and dimmeras the light turns dim so that at any time said component means exhibitone state or another corresponding to extreme conditions, and controlmeans coupled to one of said component means and responsive to one orthe other states for turning the source on or off.

1. A lighting control for turning an illuminating source on and off inresponse to ambient light conditions, comprising first photoelectricmeans responsive to the ambient light, regenerative means coupled tosaid first photoelectric means for assuming one condition when theambient light on said first photoelectric means exceeds a given valueand for assuming a second condition when the ambient light on said firstphotoelectric means is less than a given value, said regenerative meansincluding light means coupled to said first photoelectric means forturning brighter or dimmer in response to the first photoelectric means,said regenerative means further including second photoelectric meansresponsive to light from said light means and electrically coupled tosaid light means for making said light means brighter as said lightmeans turns bright and dimmer as said light means turns dim, and controlmeans coupled to said regenerative means and responsive to the conditionof said regenerative means for turning the source on or off.
 2. Acontrol as in claim 1, wherein said light means becomes brighter as saidfirst photoelectric means is subject to less ambient light.
 3. A controlas in claim 1, wherein said second photoelectric means includes aphotoelectric resistor in series with said light means and responsive tolower its resistance when subjected to more light from said light means.4. A control as in claim 2, wherein said second photoelectric meansincludes a photoelectric resistor in series with said light means andresponsive to lower its resistance when subjected to more light fromsaid light means.
 5. A control as in claim 1, wherein said firstphotoelectric means includes a voltage divider adapted to be connectedacross a voltage source and having a variable resistance photocellconnected across said light means so as to increase the voltage acrosssaid light means when the ambient light increases.
 6. A control as inclaim 3, wherein said first photoelectric means includes a voltagedivider adapted to be connected across a voltage source and having avariable resistance photocell connected across said light means so as toincrease the voltage across said light means when the ambient lightincreases.
 7. A control as in claim 1, wherein said light means includesa voltage breakdown device.
 8. A control as in claim 7, wherein saidsecond photoelectric means includes a photoelectric resistor in serieswith said light means and responsive to lower its resistance whensubjected to more light from said light means.
 9. A control as in claim7, wherein said second photoelectric means includes a photoelectricresistor in series with said light means and responsive to lower itsresistance when subjected to more light from said light means.
 10. Acontrol as in claim 7, wherein said first photoelectric means includes avoltage divider adapted to be connected across a voltage source andhaving a variable resistance photocell connected across said light meansso as to increase the voltage across said light means when the ambientlight increases.
 11. A control as in claim 1, wherein said control meansincludes third photoelectric means optically coupled and responsive tosaid light means and signal responsive means connected in series withsaid third photoelectric means, said third photoelectric meansdecreasing its resistance in response to light from said light means soas to increase the signal to said signal responsive means as said lightbecomes brighter.
 12. A control as in claim 11, wherein said signalresponsive means includes a relay coil forming a part of a relay.
 13. Acontrol as in claim 11, wherein said current responsive means includes asemiconductor switch.
 14. A control as in claim 7, wherein saidbreakdown device includes a neon lamp.
 15. A control as in claim 11,wherein said light means becomes brighter as said first photoelectricmeans is subject to less ambient light.
 16. A control as in claim 11,wherein said second photoelectric means includes a photoelectricresistor in series with said light means and responsive to lower itsresistance when subjected to more light from said light means.
 17. Acontrol as in claim 15, wherein said second photoelectric means includesa photoelectric resistor in series with said light means and responsiveto lower its resistance when subjected to more light from said lightmeans.
 18. A control as in claim 11, wherein said first photoelectricmeans includes a voltage divider adapted to be connected across avoltage source and having a variable resistance photocell connectedacross said light means so as to increase the voltage across said lightmeans when the ambient light increases.
 19. A lighting control forturning an illumination source on and off in response to ambient lightconditions, comprising photoelectric means responsive to the ambientlight, said photoelectric means assuming variable electrical conditionsin response to variatiOn of the ambient light conditions, lightcomponent means coupled to said photoelectric means for producingvarying conditions of brightness in response to changes in theelectrical condition of said photoelectric means, photoelectriccomponent means close enough to the light component means to beresponsive to light therefrom and exhibiting electrical conditions whichvary in response to light incident thereon and regeneratively coupled tosaid light component means for making the light from said lightcomponent means even brighter as the light turns bright and dimmer asthe light turns dim so that at any time said component means exhibit onestate or another corresponding to extreme conditions, and control meanscoupled to one of said component means and responsive to one or theother states for turning the source on or off.